Using natural circulation as the primary core cooling mechanism in next generation nuclear reactors provides advantages such as improved safety, less operation and maintenance costs (because of elimination of pumps), and simplicity of system. Large scale deployment of natural circulation based reactors and safety systems depend on the successful resolution of the challenges specific to natural circulation such as driving force, system pressure drops, instability effects, and critical heat flux.

In this work, natural circulation two-phase flow pressure drops in a single channel are studied experimentally. For this purpose, natural circulation hydrodynamic loop was designed. The overall pressure drop was measured by use of pressure transducer sensors and the void fraction in visible boxes which located at the end of heated tube is measured by use of high speed camera. The frictional and acceleration pressure drop are evaluated in different conditions from experimental data and corresponding theoretical formulas. The results could be useful in natural circulation based reactor design and computer codes validation.